The present invention is directed to heat transfer materials, and in particular, heat transfer materials having a fusible coating thereon.
A number of U.S. and International Patents disclose the use of cyclohexane dimethanol dibenzoate in a variety of compositions. U.S. Pat. No. 5,026,756 discloses a hot melt adhesive composition containing cyclohexane dimethanol dibenzoate as a plasticizer. U.S. Pat. No. 5,739,188 also discloses the use of cyclohexane dimethanol dibenzoate as a plasticizer in a thermoplastic composition. U.S. Pat. No. 5,795,695 discloses a xerographic transparency containing cyclohexane dimethanol dibenzoate as an adhesion promoter. U.S. Pat. No. 5,853,864 discloses disposable absorbent articles containing cyclohexane dimethanol dibenzoate as a plasticizer in an adhesive layer of the article. Further, WO 98/43822 discloses thermal dye diffusion coatings containing cyclohexane dimethanol dibenzoate. Although cyclohexane dimethanol dibenzoate has been used as a plasticizer and/or adhesion promoter in a variety of applications, the use has been limited.
In recent years, a significant industry has developed which involves the application of customer-selected designs, messages, illustrations, and the like (referred to collectively hereinafter as xe2x80x9ccustomer-selected graphicsxe2x80x9d) on articles of clothing, such as T-shirts, sweat shirts, and the like. These customer-selected graphics typically are commercially available products tailored for a specific end-use and are printed on a release or transfer paper. The graphics are transferred to the article of clothing by means of heat and pressure, after which die release or transfer paper is removed.
Heat transfer papers having an enhanced receptivity for images made by wax-based crayons, thermal printer ribbons, and impact ribbon or dot-matrix printers, are well known in the art. Typically, a heat transfer sheet comprises a cellulosic base sheet and an image-receptive coating on a surface of the base sheet. The image-receptive coating usually contains one or more film-forming polymeric binders, as well as, other additives to improve the transferability and printability of the coating. Other heat transfer sheets comprise a cellulosic base sheet and an image-receptive coating, wherein the image-receptive coating is formed by melt extrusion or by laminating a film to the base sheet. The surface of the coating or film may then be roughened by, for example, passing the coated base sheet through an embossing roll.
Much effort has been directed at generally improving the transferability of an image-bearing laminate (coating) to a substrate. For example, an improved cold-peelable heat transfer material has been described in U.S. Pat. No. 5,798,179, which allows removal of the base sheet immediately after transfer of the image-bearing laminate or some time thereafter when the laminate has cooled. Moreover, additional effort has been directed to improving the crack resistance and washability of the transferred laminate. The transferred laminate must be able to withstand multiple wash cycles and normal xe2x80x9cwear and tearxe2x80x9d without cracking or fading.
Various plasticizers and coating additives have been added to coatings of heat transfer materials to improve the crack resistance and washability of image-bearing laminates on articles of clothing. However, most plasticizers in use today are unable to significantly improve cracking without negatively impacting the washability of the coating. Cracking and fading of the transferred image-bearing coating continues to be a problem in the art of heat transfer coatings.
What is needed in the art is a heat fusible coating, which substantially resists cracking while maintaining or enhancing the washability of the coating. What is also needed in the art is a heat transfer material having a heat fusible coating thereon, wherein the heat fusible coating has improved crack resistance, fade resistance, and washability.
The present invention addresses some of the difficulties and problems discussed above by the discovery of a heat fusible coating for use on a heat transfer material, wherein the fusible coating resists cracking and fading, while having substantially no negative impact on the washability of the coated article. The heat fusible coating of the present invention comprises cyclohexane dimethanol dibenzoate, which lowers the melt viscosity of the transfer coating and provides a softer hand to the coating.
The present invention is further directed to a printable heat transfer material having a heat fusible coating thereon, wherein the heat fusible coating comprises cyclohexane dimethanol dibenzoate. The heat transfer material of the present invention comprises a base substrate and one or more coatings on a surface of the base substrate, wherein at least one coating contains cyclohexane dimethanol dibenzoate.
The present invention also is directed to a method of making a printable heat transfer material having a heat fusible coating thereon, wherein the heat fusible coating contains cyclohexane dimethanol dibenzoate. The method comprises applying cyclohexane dimethanol dibenzoate in an unfused state onto a base substrate of a heat transfer material.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
The present invention is directed to a heat fusible coating for use on a heat transfer material, wherein the fusible coating resists cracking and fading, while having substantially no negative impact on the washability of the image-bearing coating. The heat fusible coating of the present invention may be used for a number of applications, in particular, heat transfer applications.
The heat fusible coating of the present invention comprises cyclohexane dimethanol dibenzoate. The cyclohexane dimethanol dibenzoate enables the production of a heat fusible coating, which lowers the melt viscosity of the transfer coating and provides a softer hand to the coating. Cyclohexane dimethanol dibenzoate is commercially available from Velsicol(copyright) Chemical Corporation (Rosemont, Ill.) under the tradename Benzoflex(copyright) 352. Benzoflex(copyright) 352 comprises a mixture of cis and trans isomers of 1,4-cyclohexane dimethanol dibenzoate and is available in flake form.
In one embodiment of the present invention, the heat fusible coating comprises Benzoflex(copyright) 352 having a particle size smaller than the commercially available flakes. In this embodiment, the flakes of Benzoflex(copyright) 352 are ground to a desired particle size. As used herein the phrase xe2x80x9cparticle sizexe2x80x9d refers to the average dimensions (i.e., length, width, diameter, etc.) of the particles. Desirably, the heat fusible coating comprises Benzoflex(copyright) 352 particles having a particle size of less than 50 microns. More desirably, the particle size is from about 1 micron to about 30 microns. Even more desirably, the particle size is from about 2 microns to about 10 microns.
The Benzoflex(copyright) 352 particles have a melting point of about 120xc2x0 C. The particles can be incorporated into a coating composition in an unfused state, applied to a heat transfer sheet base substrate, and dried at a temperature lower than the melting point. This provides several advantages. The dried coating is readily fused when desired. Further, the unfused coating, containing the Benzoflex(copyright) 352 particles, is relatively porous, dull and tack-free, which enhances the printability of the coating. Once fused, the coating is closed, more glossy, and quite tacky, at intermediate levels of plasticizer.
The ground Benzoflex(copyright) 352 powder may be easily dispersed in water using a small amount of surfactant. Suitable surfactants include, but are not limited to, Triton(copyright) X100, a nonionic surfactant available from Union Carbide, and Tergitol(copyright) 15-S40, an ethoxylated alcohol surfactant available from BASF. The amount of surfactant may vary depending on the amount of Benzoflex(copyright) 352 particles and other mixture components. Desirably, the amount of surfactant is less than about 10 wt % of the total weight of the mixture. More desirably, the amount of surfactant is from about 1 wt % to about 5 wt % of the total weight of the mixture.
The present invention is further directed to a printable heat transfer material having a heat fusible coating thereon, wherein at least one layer of the heat fusible coating comprises cyclohexane dimethanol dibenzoate. The printable heat transfer material of the present invention comprises at least one base substrate and one or more of the following layers: a release coating layer, a tie coating layer, a base coating layer, a print coating layer, and a top coating layer. Suitable base substrates include, but are not limited to, cellulosic nonwoven webs and polymeric films. A number of suitable base substrates are disclosed in U.S. Pat. Nos. 5,242,739; 5,501,902; and 5,798,179; the entirety of which is incorporated herein by reference. Desirably, the base substrate comprises paper.
The heat transfer material of the present invention may further comprise a release coating layer. The release coating layer may be positioned next to or separate from the base substrate. The release coating layer enables cold removal of at least the base substrate from the fused coating after an image transfer is completed. Desirably, the release coating layer is adjacent to a surface of the base substrate. A number of release coating layers are known to those of ordinary skill in the art, any of which may be used in the present invention. Typically, the release coating layer comprises a thermoplastic polymer having essentially no tack at transfer temperatures (e.g. 177xc2x0 C.) and a glass transition temperature of at least about 0xc2x0 C. As used herein, the phrase xe2x80x9chaving essentially no tack at transfer temperaturesxe2x80x9d means that the release coating layer does not stick to an overlaying layer to an extent sufficient to adversely affect the quality of the transferred image. Desirably, the thermoplastic polymer comprises a hard acrylic polymer or poly(vinyl acetate). The release coating layer may further comprise an effective amount of a release-enhancing additive, such as a divalent metal ion salt of a fatty acid, a polyethylene glycol, or a mixture thereof. For example. the release-enhancing additive may be calcium stearate, a polyethylene glycol having a molecular weight of from about 2,000 to about 100,000, or a mixture thereof. Suitable release coating layers are disclosed in U.S. Pat. No. 5,798,179, the entirety of which is incorporated herein by reference.
The heat transfer material of the present invention may further comprise a tie coating layer. The tie coating layer may be positioned next to or separate from the base substrate. Desirably, the tie coating is directly above the release coating layer, when present, so as to provide a desired amount of adhesion between the release coating layer and an overlaying layer, such as a base coating layer. The tie coating layer provides an adequate amount of adhesion for manufacture, sheeting, handling, and printing of the heat transfer material, yet low enough adhesion for easy release after transfer. A number of tie coating layers are known to those of ordinary skill in the art, any of which may be used in the present invention. Suitable tie coating layers for use in the present invention are disclosed in U.S. Pat. No. 5,798,179, the entirety of which is incorporated herein by reference.
In one embodiment of the present invention, the tie coating layer of the heat transfer material comprises a powdered thermoplastic polymer, which melts in a range of from about 65xc2x0 C. to about 180xc2x0 C., and at least one film-forming binder material. Any powdered thermoplastic polymer and film-forming binder may be employed in the present invention as long as the materials meet the criteria set forth above for a tie layer coating. Suitable powdered thermoplastic polymer include, but are not limited to, polyamides, polyolefins, polyesters, ethylene-vinyl acetate copolymers, or a combination thereof. Desirably, the powdered thermoplastic polymer comprises Micropowder MPP635, a high-density polyethylene powder available from Micropowders, Inc., Tarrytown, N.Y., or Orgasol(copyright) 3501 EXDNAT 1, a 10 micron average particle size, porous copolymer of nylon-6 and nylon-12 precursors, available from Elf Atochem North America, Philadelphia, Pa. Suitable film-forming binders include, but are not limited to, water-dispersible ethylene-acrylic acid copolymers. Desirably, the film-forming binder comprises Michleman Emulsion 58035, a 35 wt % solids ethylene-acrylic acid emulsion available from Michleman Chemical Company, Cincinnati, Ohio.
In an alternative embodiment of the present invention, the tie coating layer may be a melt-extruded film. The materials of the melt-extruded film may be the same as those described above for the solution-coated, tie coating layer. Suitable melt-extrudable polymers include, but are not limited to, copolymers of ethylene and acrylic acid, methacrylic acid, vinyl acetate, ethyl acetate, butyl acrylate, polyesters, polyamides, polyurethanes, and combinations thereof. The polymer melt composition may include one or more additives. Suitable additives include, but are not limited to, waxes, plasticizers, rheology modifiers, antioxidants, anti-static agents, and anti-blocking agents. Suitable melt-extrudable tie coating layers for use in the present invention are disclosed in U.S. Pat. No. 5,798,179, the entirety of which is incorporated herein by reference.
The heat transfer material of the present invention may further comprise a base coating layer. The base coating layer may be used in combination with one or more of the above-described layers. Alternatively, the base coating layer may be used instead of the tie coating layer or both the release coating layer and the tie coating layer. The base coating layer may comprise materials similar to those described above for the tie coating layer. The base coating layer may comprise one or more powdered thermoplastic polymer and one or more film-forming binders as described above. Desirably, the base coating layer comprises from about 10 wt % to about 90 wt % of one or more powdered thermoplastic polymer and from about 90 wt % to about 10 wt % of one or more film-forming binders, based on the total weight of the dry base coating layer. More desirably, the base coating layer comprises from about 10 wt % to about 50 wt % of one or more powdered thermoplastic polymer and from about 90 wt % to about 50 wt % of one or more film-forming binders, based on the total weight of the dry base coating layer. Even more desirably, the base coating layer comprises from about 20 wt % to about 40 wt % of one or more powdered thermoplastic polymer and from about 80 wt % to about 60 wt % of one or more film-forming binders, based on the total weight of the dry base coating layer.
In one embodiment of the present invention, the base coating layer comprises powdered thermoplastic polymer in the form of high-density polyethylene powder, copolyamide particles, or a combination thereof, and a film-forming binder in the form of an ethylene-acrylic acid copolymer, a polyethylene oxide, or a combination thereof. As disclosed in U.S. Pat. No. 5,798,179, other materials may be added to the base coating layer including, but not limited to, plasticizers, surfactants, and viscosity modifiers. Desirably, the base coating layer comprises up to about 5 wt % of one or surfactants and up to about 2 wt % of one or more viscosity modifiers, based on the total weight of the dry base coating layer. Suitable surfactants include, but are not limited to, ethoxylated alcohol surfactant available from BASF under the tradename Tergitol(copyright) 15-S40 and a nonionic surfactant available from Union Carbide under the tradename Triton(copyright) X100. Suitable viscosity modifiers include, but are not limited to, polyethylene oxide available from Union Carbide under the tradename Polyox(copyright) N60K and methylcellulose.
In a further embodiment of the present invention, the base coating layer comprises cyclohexane dimethanol dibenzoate in combination with one or more powdered thermoplastic polymers and/or one or more film-forming binders. The amount of cyclohexane dimethanol dibenzoate in the base coating layer may vary depending on the overall coating composition. Desirably, the amount of cyclohexane dimethanol dibenzoate in the base coating layer is up to about 90 wt % based on the total weight percent of the dry base coating layer. More desirably, the amount of cyclohexane dimethanol dibenzoate in the base coating layer is from about 10 wt % to about 50 wt % based on the total weight percent of the dry base coating layer.
When the base coating layer contains cyclohexane dimethanol dibenzoate, one or more powdered thermoplastic polymers, and one or more film-forming binders, the base coating layer desirably comprises from about 10 wt % to about 90 wt % cyclohexane dimethanol dibenzoate, from about 90 wt % to about 10 wt % of one or more powdered thermoplastic polymers, and from about 90 wt % to about 10 wt % of one or more film-forming binders, based on the total weight percent of the dry base coating layer. More desirably, the base coating layer comprises from about 10 wt % to about 50 wt % cyclohexane dimethanol dibenzoate, from about 50 wt % to about 10 wt % of one or more powdered thermoplastic polymers, and from about 70 wt % to about 40 wt % of one or more film-forming binders based on the total weight percent of the dry base coating layer. As disclosed above, other materials may be added to this base coating layer including, but not limited to, plasticizers, surfactants, and viscosity modifiers.
Similar to the tie coating layer above, the base coating layer may be in the form of a melt-extruded film. The extruded film may comprise one or more of the materials described above including the cyclohexane dimethanol dibenzoate. In one embodiment of the present invention, an extruded base coating layer comprises a co-extruded film having a layer of Nucrel(copyright) KC500, an ethylene/methacrylic acid copolymer having a melt index of 500 available from Dupont, and a layer of Primacor(copyright) 59801, an ethylene-acrylic acid copolymer having a melt index of 200 available from Dow Chemical Company.
In addition to the layers mentioned above, the heat transfer material of the present invention may comprise a print coating layer. The print coating layer provides a print surface for the heat transfer sheet. The print coating layer is formulated to minimize feathering of a printed image and bleeding or loss of the image when the transferred image is exposed to water. Suitable print coating components include, but are not limited to, cyclohexane dimethanol dibenzoate, particulate thermoplastic materials, film-forming binders, a cationic polymer, a humectant, ink viscosity modifiers, weak acids, and surfactants.
The print coating layer may contain one or more thermoplastic particles. Desirably, the particles have a largest dimension of less than about 50 micrometers. More desirably, the particles have a largest dimension of less than about 20 micrometers. Suitable powdered thermoplastic polymers include, but are not limited to, polyolefins, polyesters, polyamides, and ethylene-vinyl acetate copolymers.
The print coating layer may also contain one or more film-forming binders. Desirably, the one or more film-forming binders are present in an amount of from about 10 to about 50 weight percent, based on the weight of the thermoplastic polymer. More desirably, the amount of binder is from about 10 to about 30 weight percent. Suitable binders include, but are not limited to, polyacrylates, polyethylenes, and ethylene-vinyl acetate copolymers. Desirably, the binders are heat-softenable at temperatures of less than or about 120xc2x0 C.
Further, the print coating layer may comprise a cationic polymer. Desirably, the cationic polymer is present in an amount from about 2 to about 20 weight percent, based on the weight of the thermoplastic polymer. Suitable cationic polymers include, but are not limited to, an amide-epichlorohydrin polymer, polyacrylamides with cationic functional groups, polyethyleneimines, and polydiallylamines.
One or more other components may be used in the print coating layer, such as a humectant and a viscosity modifier. For example, the print coating layer may contain from about 1 to about 20 weight percent of a humectant, based on the weight of the thermoplastic polymer. Suitable humectants include, but are not limited to, ethylene glycol and poly(ethylene glycol). Desirably, the poly(ethylene glycol) has a weight-average molecular weight of from about 100 to about 40,000. More desirably, the poly(ethylene glycol) has a weight-average molecular weight of from about 200 to about 800. In addition, the print coating layer may contain from about 0.2 to about 10 weight percent of an ink viscosity modifier, based on the weight of the thermoplastic polymer. Desirably, the viscosity modifier comprises a poly(ethylene glycol) having a weight-average molecular weight of from about 100,000 to about 2,000,000. More desirably, the poly(ethylene glycol) has a weight-average molecular weight of from about 100,000 to about 600,000.
The print coating layer may also include a weak acid and/or a surfactant. As used herein, the term xe2x80x9cweak acidxe2x80x9d refers to an acid having a dissociation constant less than one (or a negative log of the dissociation constant greater than 1). Desirably, the weak acid is present in an amount from about 0.1 to about 5 weight percent based on the weight of the thermoplastic polymer. Desirably, the weak acid is citric acid. Suitable surfactants include anionic, nonionic, or cationic surfactants. Desirably, the surfactant is a nonionic or cationic surfactant. Examples of anionic surfactants include, but are not limited to, linear and branched-chain sodium alkylbenzenesulfonates, linear and branched-chain alkyl sulfates, and linear and branched-chain alkyl ethoxy sulfates. Cationic surfactants include, but are not limited to, tallow trimethylammonium chloride. Examples of nonionic surfactants. include, but are not limited to, alkyl polyethoxylates, polyethoxylated alkylphenols, fatty acid ethanol amides, complex polymers of ethylene oxide, propylene oxide, and alcohols, and polysiloxane polyethers. More desirably, the surfactant is a nonionic surfactant.
In one embodiment of the present invention, the print coating layer comprises one or more of the above-described components and cyclohexane dimethanol dibenzoate. The amount of cyclohexane dimethanol dibenzoate in the print coating layer may vary depending on the overall coating composition. Desirably, the amount of cyclohexane dimethanol dibenzoate in the print coating layer is up to about 50 wt % based on the total weight percent of the dry coating layer. More desirably, the amount of cyclohexane dimethanol dibenzoate in the print coating layer is from about 10 wt % to about 30 wt % based on the total weight percent of the dry coating layer. Even more desirably, the amount of cyclohexane dimethanol dibenzoate in the print coating layer is from about 15 wt % to about 25 wt % based on the total weight percent of the dry coating layer.
In a further embodiment of the present invention, the print coating layer comprises a microporous polyamide powder, an ethylene-acrylic acid copolymer binder, a dispersent (Klucel(copyright) L hydroxyethyl cellulose), a surfactant (Triton(copyright) X100), a buffer (sodium carbonate) and cyclohexane dimethanol dibenzoate. The print coating layer has a porous surface for absorption of ink jet inks.
The heat transfer sheet of the present invention may further comprise a top coating layer. The top coating layer functions as a wetting agent and an ink viscosity modifier. Desirably, the top coating layer comprises one or more cationic polymers. Suitable cationic polymers include, but are not limited to, poly(N,N-dimethylethylamino methacrylate), quaternized with methyl chloride, sold under the tradename, Alcostat(copyright) 567 from Allied Colloids. Other materials may be added to the top coating layer including, but not limited to, plasticizers, surfactants, and viscosity modifiers. Suitable viscosity modifiers include, but are not limited to, polyethylene oxide available from Union Carbide under the tradename Polyox(copyright) N60K and methylcellulose.
The image-bearing coating of the heat transfer sheet, comprising one or more of the above-described coating layers, may be transferred to an article of clothing, or other porous substrate, by applying heat and pressure to the coating. Desirably, the imaged-bearing coating of the heat transfer sheet melts and penetrates into the interstices of the substrate, as opposed to merely coating the substrate surface. In order to penetrate into a fabric, the combined thickness of the tie, base, print and top coating layers is desirably greater than 1.0 mil. More desirably, the combined thickness of the tie, base, print and top coating layers is about 1.5 to about 2 mils.
The present invention also is directed to a method of making a printable heat transfer material having a heat fusible coating thereon, wherein the heat fusible coating contains cyclohexane dimethanol dibenzoate. The method comprises applying cyclohexane dimethanol dibenzoate in an unfused state onto a base layer of a heat transfer material. In one embodiment of the present invention, one or more of the above-described coating compositions are applied to the base layer by known coating techniques, such as by roll, blade, and air-knife coating procedures. Each individual coating may be subsequently dried by any drying means known to those of ordinary skill in the art. Suitable drying means include, but are not limited to, steam-heated drums, air impingement, radiant heating, or a combination thereof. In an alternative embodiment, one or more of the above-described coating layers may be extrusion coated onto the surface of the base layer or a coating thereon. Any extrusion coating techniques, well known to those of ordinary skill in the art, may be used in the present invention.
If desired, any of the foregoing coating layers may contain other materials, such as processing aids, release agents, pigments, deglossing agents, antifoam agents, and the like. The use of these and similar materials is well known to those having ordinary skill in the art. The layers, which comprise a film-forming binder, may be formed on a given layer by known coating techniques, such as by roll, blade, and air-knife coating procedures. The resulting heat transfer material may then be dried by any drying means known to those of ordinary skill in the art. Suitable drying means include, but are not limited to, steam-heated drums, air impingement, radiant heating, or a combination thereof.